Embodiments according to the invention relate to wireless communication system and particularly to an apparatus and a method for controlling a node of a wireless communication system.
In a MIMO-capable base station, each of the antennae that constitutes the MIMO system is connected to a power amplifier that provides the needed amplification for transmitting and receiving the analog signals. Baseband processing is usually performed in a common block that is shared by all the antennae. Referring to FIG. 3, it is evident from it that up to 80% of the overall energy consumption of a base station comes from the power amplifier (see for example “L. Saker, S-E. Elayoubi and H. O. Scheck, System selection and sleep mode for energy saving in cooperative 2G/3G networks, IEEE VTC-fall 2009, Anchorage, September 2009”).
On the other hand, it has also been shown that minimizing the usage of the power amplifiers still does not provide any benefit in terms of reduction of energy consumption (see “Micallef, G.; Mogensen, P.; Scheck, H.-O., “Cell Size Breathing and Possibilities to Introduce Cell Sleep Mode”, in Proc. of European Wireless 2010, Lucca, Italy”). This is due to the design choices of the current power amplifiers, which need a lot power supply even when they are not actively used.
FIG. 4 shows the impact of the traffic pattern on energy consumption. As it can be seen from it, in low load conditions, the base station operation consumes a lot of energy. The base station hardware in fact is usually tailored to be efficient only at high traffic loads, being dimensioned to provide the needed capacity also during the traffic peaks.
Putting these considerations in relation to a 24 hours mobile traffic scenario (FIG. 2), as measured in real UMTS cells, it can already be seen how big the room can be for energy improvement in cellular systems.
Base station networking has attracted a lot of research attention recently, due to the relevant benefits achievable in terms of wireless transmission capacity, inter-cell interference management and reduction of energy consumption at the individual cell sites.
Referring to energy efficiency of the mobile network, the use of base station sleeping modes triggered by traffic load analysis has been proposed in some recent research papers (see for example “Jie Gong, Sheng Zhou, ZhishengNiu, Peng Yang, “Traffic-aware base station sleeping in dense cellular networks”, in Proc. of IEEE IWQOS 2010”, “Sheng Zhou, Jie Gong, Zexi Yang, ZhishengNiu and Peng Yang, “Green Mobile Access Network with Dynamic Base Station Energy Saving”, in Proc. of ACM Mobicom 2009” and “LouaiSaker, Salah-EddineElayoubi, TijaniChahed, “Minimizing energy consumption via sleep mode in green base station”, in Proc. of IEEE 2010) and network vendors' works (see for example “Micallef, G.; Mogensen, P.; Scheck, H.-O., “Cell Size Breathing and Possibilities to Introduce Cell Sleep Mode”, in Proc. of European Wireless 2010, Lucca, Italy” and “Green Radio, “NEC's Approach towards Energy-efficient Radio Access Networks”. Whitepaper, February 2010”). The idea behind the enabling of sleeping modes at base station is to back up the needed coverage/capacity of the sleeping base station by enlarging the coverage area of one or more surrounding ones.
There are also some local approaches, which use, for example, a scheduling with a queue, which waits and transmits when the channel is good as shown for example in FIG. 5. Other configurations can range from MIMO (multiple input multiple output) up to SISO (single input single output) configurations, as shown for example in FIG. 6. Each mobile device 610 is addressed by only one antenna 620 of the base station 630.
There are distributed and centralized approaches, as for example, a coordination between base stations for energy saving, which switches off some base station sites and provides a same coverage, which is called cell breathing technique (increased transmit range of some neighbor cells). An example for four base stations 710 with one deactivated base station 720 is shown in FIG. 7.
In “Jie Gong, Sheng Zhou, ZhishengNiu, Peng Yang, “Traffic-aware base station sleeping in dense cellular networks”, in Proc. of IEEE IWQOS 2010”, the authors propose a sleeping-mode scheme that switches off some base stations when the traffic load is low. The constraint the authors introduce is based on the guaranteeing of a certain blocking probability. The authors also propose a minimum sleeping-mode holding time to avoid frequent on/off switching at base stations.
In “LouaiSaker, Salah-EddineElayoubi, TijaniChahed, “Minimizing energy consumption via sleep mode in green base station”, in Proc. of IEEE 2010”, two radio allocation schemes are proposed that activate resources only when they are needed to satisfy user demand and QoS requirement. The first scheme is dynamic. It switches resources ON and OFF as a function of the instantaneous change of the load in the system, which in turn follows the users arrivals and departures. The second scheme is semi-static. It activates and deactivates resources when the mean traffic load varies in the system.
In “S. Zhou, J. Gong, Z. Yang, Z. Niu, and P. Yang, “Green mobile access network with dynamic base station energy saving,” MobiCom '09 poster, September 2009”, dynamically turning off certain BS is considered when the network traffic is low. Centralized and decentralized implementations are investigated. The assumption is that all the channel information and the traffic requirements is known at the network side. Energy efficiency of the proposed algorithms and the tradeoff between energy saving and coverage guarantee.